pH is a measure of the acidity of alkalinity of a solution or substance. Solutions with a pH less than seven are considered acidic, while those with a pH greater than seven are considered basic or alkaline. A pH level of 7.0 is considered neutral. When a pH level is 7.0, it is defined as ‘neutral’ because at this pH the concentration of H3O+ equals the concentration of OH− in pure water. The pH value is a measure of the activity of hydrogen ions in the solution. The pH scale is typically between 1 and 14 with 1 being the most acidic and 14 the most alkaline. The pH scale is an inverse logarithmic representation of hydrogen proton concentration. Therefore a value change of 1 pH unit represents a factor of 10 increase or decrease.
The vagina is the muscular canal extending from the vaginal opening to the cervix and consists of three layers of tissue. The mucosa is the surface layer and consists of mucus membranes. The next layer of tissue is a layer of muscle concentrated mostly around the outer third of the vagina. The third layer is the innermost layer and consists of fibrous tissue.
The vagina contains folds or wrinkles rather than a smooth surface. It is usually about 3 to 5 inches in length and its walls are lined with a mucus membrane. The vagina includes numerous tiny glands that generate vaginal secretions/fluids. The vaginal walls are continually producing secretions/fluids necessary to provide lubrication, to cleanse the vagina and to maintain the proper acidity to prevent infection. The vagina tends to be fairly acidic usually in the range of 3.5 to 4.5 pH. The walls of the vagina are normally in contact with each other, which is contrary to most anatomical illustrations. When something enters the vagina, its walls separate to make room for the object. Because of its muscular tissue, the vagina has the ability to expand and contract adjusting to fit snugly around the object inserted.
Accurate monitoring of vaginal pH is an important part of in the diagnosis of vaginal infections such as Bacterial Vaginitis (BV). The normal vaginal pH in reproductive age women is usually 3.5 to 4.5. A value greater the 4.5 can indicate a variety of vaginal infections which are usually accompanied by unusual discharge, itching, burning and irritation. The three diseases most frequently associated with vaginal discharge are BV, trichomoniasis (caused by a sexually transmitted infectious parasite), and candidiasis (usually caused by Candida albicans).
Bacterial vaginosis (BV) is the most common cause of vaginal infection. BV is caused by an imbalance of naturally occurring bacterial flora. To control bacterial growth, the vagina is normally slightly acidic with a pH of 3.5-4.5. A pH greater than 4.5 is considered alkaline and is suggestive of bacterial vaginosis.
Candidiasis, also known as a “yeast infection” or VVC, is a common fungal infection that occurs when there is overgrowth of the fungus called Candida. Candida is always present in the body in small amounts, however when an imbalance occurs, such as when the normal acidity of the vagina changes or when hormonal balance changes, Candida can multiply. When that happens, symptoms of candidiasis appear.
Trichomoniasis, sometimes referred to as “trich,” is a common cause of vaginitis. Trichomoniasis is primarily an infection of the urogenital tract with the most common site of infection the vagina or urethra in women. With a trichomonas infection, the vagina is likely to be more alkaline than normal. An estimated five million cases of trichomoniasis occur each year in the United States. Men also can contract trichomoniasis however do not often have signs or symptoms. Some men may temporarily have an irritation inside the penis, mild discharge, or slight burning after urination or ejaculation.
According to the Centers for Disease Control (CDC), there are some serious risks from BV such as;                An increase in a woman's susceptibility to HIV infection if she is exposed to HIV virus.        An increase in the chances that an IHV-infected woman can pass HIV to her sex partner.        An increase in a woman's susceptibility to other STDs, such as herpes simples virus (HSV) Chlamydia and gonorrhea.        An increase in the development of an infection following surgical procedures such as a hysterectomy or an abortion.        During pregnancy, an increase in adverse pregnancy outcomes has been detected, including premature rupture of the membranes, preterm labor, preterm birth, intraamniotic infection, and postpartum endometritis.        
The results of several investigations indicate that treatment of pregnant women with BV who are at high risk for preterm delivery (i.e., those who previously delivered a premature infant) might reduce the risk for prematurity. Monitoring of pH level during pregnancy is an important criterion in reducing the incidences of Preterm labor and birth. Studies have shown that bacterial vaginosis was associated with the preterm delivery of low-birth-weight infants independently of other recognized risk factors. Reduction in the instances of pre-mature birth improves the health of the newborn and significantly reduces the cost of care.
Oral clindamycin prevents spontaneous preterm birth and mid trimester miscarriage in pregnant women with bacterial vaginosis. Based on estimates from the CDC, the number of pregnant women in the United States alone that are annually infected with BV is 1,080,000 and Trichomoniasis is 124,000.
Untreated bacterial vaginosis is a risk factor for post abortion pelvic inflammatory disease (PID). Studies have shown that preabortal screening and subsequent treatment of those who test clinically positive does lower the incidence of postabortion PID.
BV can be diagnosed by the use of clinical criteria or Gram stain. In clinical practice BV is diagnosed using the Amsel criteria. Clinical criteria require typically three of the following symptoms or signs:                homogeneous, thin, white discharge that smoothly coats the vaginal walls;        presence of clue cells on microscopic examination;        pH of vaginal fluid>4.5; and        a fishy odor of vaginal discharge before or after addition of 10% KOH (i.e., the whiff test).        
Current methods of monitoring vaginal pH include various methods of checking pH paper type products. The accuracy of these products are generally in the range of 0.3 pH to 0.5 pH. They generally require the user to subjectively compare color in order to determine the pH value and are subject to inaccuracies. Inaccuracies can be due to lighting conditions or the ability of the user to accurately compare color. Manual recording of the subjective readings is required.
The cervix is the lower portion of the uterus and forms the neck of the uterus. The cervix joins with the top end of the vagina and the uterine cavity. The cervix protrudes into the vagina and this area is called the ectocervix. Typically the ectocervix is about 2.5 to 3 cm in diameter and has an elliptical surface. The ectocervix is also called the external os. The size and shape of the external os can vary widely depending on the age of the woman or if she has given vaginal birth. The passage way between the external os and the uterus is referred to as the endocervical canal. The endocervical canal terminates at the internal os which is the opening of the cervix inside the uterine cavity. The cervical canal of the uterus is covered by a thin layer of mucus. Pockets within the lining of the cervix function to produce cervical fluid.
Studies by George I. Gorodeski et al, such as those disclosed in U.S. Patent Application US/2008/0071190 published Mar. 20, 2008, show that cervical pH changes dramatically during the ovulation cycle while the vaginal pH remains relatively constant. The in-vivo vaginal and cervical pH values recorded were measured in Gorodeski by attaching a strip of pHydrion paper at the tip of uterine forceps. In addition, another more complicated clinical lab test was preformed by measuring cell cultures of the human Ecto-cervical Epithelial cells and human Endocervical cells. These tissue samples were collected and then analyzed and measured using an elaborate clinical procedure. Using these techniques, it was shown that the pH of the ectocervix changes as much as 2 pH during the ovulation cycle with the peak occurring during days 11-14 Of the cycle (ovulation period). During the same periods the vaginal readings remained relatively constant.
Studies have also shown that monitoring of vaginal pH can be a good indicator of menopause in women who are without vaginitis and are not receiving estrogen therapy. A pH reading greater than 4.5 could indicate menopause and the need for estrogen therapy. Low levels of estrogen can cause elevated pH levels in the area of 6.0 or higher. The sensitivity of FSH blood work was no different than vaginal pH in the diagnosis of menopause. Estrogen causes deposition of glycogen in mature epithelial cells, which is then converted by bacterial enzymes to glucose. The glucose is anaerobically fermented to lactic acid, which gives the vagina a pH of 3.5 to 4.5.
Further studies have shown that an important function of the vaginal and cervical epithelial cells is to regulate the pH of the lumen of the lower genital tract. During premenopausal years vaginal luminal pH ranges between 4.5 and 6.0 with mild alkalinization to about 6.5 before ovulation. Lack of estrogen, such as after menopause, is associate with alkalinization to about 6.5-7.0, whereas replacement with estrogen can acidify the luminal vaginal pH to about 5.5.
On a related note, there are times when urine pH can indicate serious health issues. For example, a very high (alkaline) urine pH could be caused by kidney failure or a urinary tract infection. A very low (acidic) urine pH could be the result of lung disease, complications of diabetes, starvation, or diarrhea. The glomerular filtrate of blood is usually acidified by the kidneys from a pH of approximately 7.4 to a pH of about 6 in the urine. Depending on the person's acid-base status, the pH of urine may range from 4.5 to 8. The kidneys maintain normal acid-base balance primarily through the reabsorption of sodium and the tubular secretion of hydrogen and ammonium ions. Urine becomes increasingly acidic as the amount of sodium and excess acid retained by the body increases. Alkaline urine, usually containing bicarbonate-carbonic acid buffer, is normally excreted when there is an excess of base or alkali in the body. Secretion of acidic or alkaline urine by the kidneys is one of the most important mechanisms the body uses to maintain a constant body pH.
A highly acidic urine pH occurs in:                Acidosis        Uncontrolled diabetes        Diarrhea        Starvation and dehydration        Respiratory diseases in which carbon dioxide retention occurs and acidosis develops        
A highly alkaline urine occurs in:                Urinary tract obstruction        Pyloric obstruction        Salicylate intoxication        Renal tubular acidosis        Chronic renal failure        Respiratory diseases that involve hyperventilation (blowing off carbon dioxide and the development of alkalosis)        
Urine pH is often used to monitor a person's diet. In people who are not vegetarians, the of urine tends to be acidic. A diet rich in citrus fruits, legumes, and vegetables raises the pH and produces urine that is more alkaline. Generally an accurate measurement of urinary pH can be done only on a freshly voided specimen. If urine pH is to be useful, it is necessary to use pH information in comparison with other diagnostic information.